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RISS 인기검색어
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- 저자 : Marta I. Litter (검색결과 4 건)
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Heterogeneous photocatalytic degradation of gallic acid under different experimental conditions
Quici, Natalia,Litter, Marta I. Korean Society of Photoscience 2009 Photochemical & photobiological sciences Vol.8 No.7
UV/$TiO_2$-heterogeneous photocatalysis was tested as a process to degrade gallic acid (Gal) in oxygenated solutions at pH 3. In the absence of oxidants other than oxygen, decay followed a zero order rate at different concentrations and was slow at concentrations higher than 0.5 mM. Addition of $Fe^{3+}$, $H_2O_2$ and the combination $Fe^{3+}/H_2O_2$ improved Gal degradation. In the absence of $H_2O_2$, an optimal Fe:Gal molar ratio of 0.33:1 was found for the photocatalytic decay, beyond which addition of $Fe^{3+}$ was detrimental and even worse in comparison with the system in the absence of $Fe^{3+}$. $TiO_2$ addition was beneficial compared with the same system in the absence of the photocatalyst if $Fe^{3+}$ was added at low concentration (0.33:1 Fe:Gal molar ratio), while at high concentration (1:1 Fe:Gal molar ratio) $TiO_2$ did not exert any significant effect. $H_2O_2$ addition (1:0.33 Gal:$H_2O_2$ molar ratio, absence of Fe(III)) also enhanced the heterogeneous photocatalytic reaction. Simultaneous addition of $Fe^{3+}$ and $H_2O_2$ was more effective than the addition of the separate oxidants. This system was compared with Fenton and photo-Fenton systems. At low $H_2O_2$ concentration (0.33:1:0.2 Fe:Gal:$H_2O_2$ molar ratio), the presence of $TiO_2$ also enhanced the reaction. The influence of the thermal charge transfer reaction between Gal and Fe(III), which leads to an important Gal depletion in the dark with formation of quinones, was analysed. The mechanisms taking place in these complex systems are proposed, paying particular attention to the important charge transfer reaction of the Fe(III).Gal complex operative in dark conditions.
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Meichtry, Jorge M.,Rivera, Veronica,Di Iorio, Yesica,Rodriguez, Hernan B.,Roman, Enrique San,Grela, Maria A.,Litter, Marta I. Korean Society of Photoscience 2009 Photochemical & photobiological sciences Vol.8 No.5
Hydroxoaluminiumtricarboxymonoamide phthalocyanine (AlTCPc) adsorbed at different loadings on $TiO_2$ Degussa P-25 was tested for Cr(VI) photocatalytic reduction under visible irradiation in the presence of 4-chlorophenol (4-CP) as sacrificial donor. A rapid reaction takes place in spite of the presumable aggregation of the dye on the $TiO_2$ surface. The removal of Cr(VI) is fairly negligible under visible-light irradiation, either without photocatalyst or in the presence of bare $TiO_2$. The fast capture of conduction band electrons by Cr(VI), which forms a surface complex with $TiO_2$, inhibits the formation of reactive oxygen species in the reductive pathway. This fact and the easier oxidation of 4-CP as compared to AlTCPc hinder the photobleaching of the dye and make feasible Cr(VI) reduction under visible irradiation. The consumption of Cr(VI) follows a pseudo-first order kinetics; the decay constant depends, in the studied range, on the photocatalyst mass, but it is barely affected by dye loading. The presence of 4-CP is essential, but its concentration has no effect on the Cr(VI) decay rate. Oxidation products of 4-CP, such as hydroquinone, catechol or benzoquinone, are not observed. Direct evidence of the one-electron reduction of Cr(VI) to Cr(V) was obtained by EPR spectroscopy using citric acid as Cr(V) trapping agent. In this case, disappearance of Cr(V) also follows a first order decay, but conduction band electrons do not seem to be involved. The fact that oxidation products of 4-CP are not observed is consistent with the fast dark removal of reaction intermediates by Cr(V), proved by EPR.
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Features and Efficiency of Some Platinized TiO₂ Photocatalysts
Emilio, Carina A.,Testa, Juan J.,Hufschmidt, Dirk,Colo´n, Gerardo,Navio´, Jose´ A.,Bahnemann, Detlef W.,Litter, Marta I. 한국공업화학회 2004 Journal of Industrial and Engineering Chemistry Vol.10 No.1
Three commercial powdered photocatalysts, Degussa P25 (P25), Sachtleben Hombikat UVlOO (WlOO) and Millennium TiONA PC 50 (PC50) have been platinized to incorporate 0.5 and 1 wt.% Pt on the surface of the particles. The physicochemical properties (SBET, particle size, morphology of the particles, etc.) have been measured and compared among the samples. The photocatalytic efficiency has been tested with two environmentally important oligocarboxylic acids, EDTA and NTA (5 mM). No strong differences could be observed among the catalysts in the case of EDTA, and an inhibition was observed in all cases. A striking effect of platinization has been observed in the case of NTA degradation, with a change in the kinetics from zero order in the pure precursors to first order in the platinized samples. Pure and platinized HB samples were the best photocatalysts for NTA. An optimum Pt amount (0.5 wt.%) was observed for the photoefficiency of the samples. It can be concluded that the efficiency is more dependent on the nature of the substrate to be degraded than on the physicochemical properties of the samples
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